[R] multiple moderated regression steps

Frank Harrell f.harrell at vanderbilt.edu
Fri Jul 1 15:22:31 CEST 2011

How does it help to center the variables?  What statistical principles are
you using to fit your model and how are you ensuring statistical validity of
inferential estimates?  Why do it in multiple steps?  Why use a mixture of
software tools?  What is the utility of standardized regression

stamkiral wrote:
> hi,
> ım studying moderated effects of percieved social support and justice
> world belief on relationship between stress coping strategies and
> depression level. ı haver never run this analysis before soi ı want to
> check my steps whether correct or not. 
> first ı run regression 
> in step 1 
> centered independent variables and centered moderators
> in step2
> two way interactions
> instep 3
> three way interactions
> as results ı found significiant two way and three way interactions. "It 
> ıs important after this"
> for example two way interactions;
> ı run 2 slopes that fit in with Winnifred's suggestion
> (http://www.docstoc.com/docs/21151269/Moderated-Multiple-Regression-v5
> p.6) 
> my criteria for significence was the centered indipendent vairable (that
> has significant interaction level) in Block 2--------- is this way is
> correct?????
> second to plot this slope ı used Dawson' s 2 way unstandardised excel
> spreadsheet (http://www.jeremydawson.co.uk/slopes.htm). In spreadsheet it
> is required to enter unstandardised regression coefficients of IV,
> moderator and interaction. ın which block the coefficients are true for
> entering IV and moderator co efficients?????
> ın 1 block (that include main effects) or in 2 block (that include
> interactions)?????
> one more question: In three way spreadshhet it is necessary to enter
> variance of IV*Moderator coefficient. ın matrıx which covariance block is
> correct to enter this value? should ı look at second covariance block or
> third covariance block.
> like this,for value of Covariance of IV*Mod1, IV*Mod2 coefficients which
> covariance block must be taken as correct??? 
> thaks so much
> Note: excuse me for my English 

Frank Harrell
Department of Biostatistics, Vanderbilt University
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